Re: [ATM] spherometer

["Bob May" <rmay@nethere.com>]

Commercially available spherometers are not cheap!!!  The best is
to buy a dial indicator and build your own base for it.  I'vegot
the formula for figruing out the actual diameter of the
spherometer on my webpages so take a look there.
As to which to get, there are several accuracy ratings for them.
The dial indicator is a standard item for the machinist and you
can generally find them everywhere that machinists buy their
tools.  The best is the most accurate ones, the ones and the
travel doesn't need to be that large for measuring most stuff.
On my spherometer, the reading is usually between 0.010 to 0.25"
for most telescope mirrors. This means that a 0.050" travel
indicator  can be used if that is what is available.
I'd also suggest that you try the used machinery places first as
they may have one for a lot less than a new one.

Bob May
may dot astronomy.net

----- Original Message -----
From: horace r davis <hrd9@juno.com>
To: <atm@atmlist.net>
Sent: Thursday, March 13, 2008 5:32 AM
Subject: [ATM] spherometer


> where is a good place to by one and is .001 ok or does it need
to go to
> .0001 to measure the mirror.
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